Soft Sketch: Material Tests

HEATING ELEMENT AND MATERIAL TESTS

There were several material tests that I conducted before I knew which will ones would work best.

The first material I needed to figure out was what I was going to use for a heating element.

Steel wool is conductive and also highly resistive, enough so, that I have used it before in a project using thermochromic inks and once given power heated up very nicely. However, it is also extremely flammable because of this nature, so although I knew it to work, it was still a material that would need to be handled thoughtfully.

I tested it in two ways, I used it raw by needle felting it into the sheep’s wool into squares and second, I mixed it with the wool and cut that into squares.

The raw steel wool got too hot, on the verge of catching fire, and the mixed squares were too slow. Also the pixels themselves were not insulated enough causing the heat to dissipate through out the grid so no discernible pixel was evident.

What was then suggested to me was nichrome, the heating element within toasters and hair dryers. This sounded extremely promising, so I ordered some from United Nuclear and while I was waiting for arrival took the opportunity to crack open some light bulbs in order to snatch the filament for some preliminary tests. I would like to add that you can find spools of nichrome elsewhere that would be more economical if you are looking for more than 10 feet.

Cracking open the lightbulbs was easier than I thought, but still challenging.

What had occurred to me through this process was that I would need a piece of low resistant metal to sandwich the nichrome in-between. I went to metalliferous and searched for the thinnest, smallest piece of metal I could find. I found 18 ga. .5″ squares that I immediately vetoed because of the thickness. I went for the 24 ga. nickel/silver and copper circles with a .375″ diameter. I also chose to use thermal adhesive to fasten the very thin piece of nichrome and help dissipate the heat. There are two kinds of adhesive that Arctic Silver produce, one of the same name primarily made of silver and Arctic Alumina made of aluminum oxide and boron nitride (ceramics) . I chose the latter because of it’s insulative qualities and it is neither electrically conductive nor capacitive.

Feeling really confident of this combination of elements, I set out to make a pixel prototype. The one that I would build the other 35 after.

What’s pictured above is a pixel made with the copper disks, it worked really well, but was really heavy. I eventually tried copper foils, which was too fragile and finally tried copper based fabric I purchased from lessemf.com. After all the trials , the fabric turned to be superior through feel and durability.

NEXT CHAPTER – Building the Soft Circuit